1. Field of the Invention
The present invention relates to an atomic layer deposition apparatus using a neutral beam and a method of depositing an atomic layer using the apparatus, and more particularly, to an atomic layer deposition apparatus using a neutral beam and a method of depositing an atomic layer using the apparatus in which a second reaction gas is ionized to form plasma, and a resulting flux of radicals, i.e. an ion beam, is neutralized and radiated onto a substrate to be treated.
2. Description of the Prior Art
Due to increasing demand for highly integrated semiconductor devices, recent years have seen continuous reduction of a semiconductor integrated circuit design rule to the point of a critical dimension not more than 90 nm. Nowadays, in order to implement such nanometer-scale semiconductor devices, ion enhancement equipment such as a high density plasma apparatus, a reactive ion etcher, and so on are being widely used. However, such equipment may cause physical and electrical damage to a semiconductor substrate or a specific material layer on the semiconductor substrate, since it involves vast quantities of ions for performing an etching (or deposition) process colliding with the semiconductor substrate or specific material layer with hundreds eV of energy.
For example, the surface layer of a crystalline substrate or a specific material layer bombarded with ions may be converted into an amorphous layer, some incident ions are adsorbed or some components of the bombarded material layer are selectively decomposed, so that the chemical composition of an etched (or deposited) surface layer is changed. In addition, atomic bonds of the surface layer are damaged by the bombardment, thereby becoming dangling bonds. Such dangling bonds may cause physical or electrical damage to the material, or give rise to charge-up damage of a gate insulating layer or electrical damage by notching of polysilicon due to charging of photoresist. In addition to such physical and electrical damage, there occurs either surface contamination caused by a chamber material, or surface contamination caused by reaction gases such as C—F polymers generated when using a CF-based reaction gas.
Therefore, since the physical/electrical damage caused by such ions in the nanometer-scale semiconductor devices decreases reliability and productivity of the semiconductor devices, it is required to develop an innovative semiconductor etching (or depositing) apparatus and method that may be applied in the future according to the trend of the high integration of the semiconductor devices and resulting reduction of the design rule.
As an example of such requirement, D. B. Oakes et al. propose a damage-free etching technology using a hyperthermal atomic beam in the paper titled “Selective, Anisotropic and Damage-Free SiO2 Etching with a Hyperthermal Atomic Beam.” As another example, Takashi Yunogami et al. propose a silicon oxide etching technology with little damage using a neutral beam and a neutral radical in the paper titled “Development of Neutral-Beam-Assisted Etcher” (J. Vac. Sci. Technol. A 13(3), May/June, 1995). For still another example, M. J. Goeckner et al. propose an etching technology using an overheated, charge-free neutral beam instead of plasma in the paper titled “Reduction of Residual Charge in Surface-Neutralization-Based Beams” (2nd International Symposium on Plasma Process-Induced Damage, May 13-14, 1997, Monterey, Calif.).
In the process of fabricating the semiconductor devices, a sputtering method, a chemical vapor deposition (CVD) method, and an atomic layer deposition (ALD) method are generally employed in order to uniformly deposit a thin layer. In the sputtering method, an inert gas such as argon is converted into plasma to sputter a target surface, thereby forming a highly pure, thin layer having excellent adhesion. However, the sputtering method makes it very difficult to obtain uniformity across the entire thin layer.
In the CVD method, most widely used nowadays, various gases are supplied and induced by high energy in the form of intense heat, light, or plasma to chemically react to form a thin layer of desired thickness. While CVD has the advantages of excellent step coverage and high yield, a temperature of the thin layer during its formation is very high, and the thickness of the thin layer cannot be controlled to a precision of several Å. In addition, since at least two kinds of reaction gas are simultaneously supplied into a reactor, particles may be generated, which may be a source of contamination.
Meanwhile, in the ALD method, a reaction gas and a purge gas are alternately supplied to deposit a thin layer one atomic layer unit at a time. The precise thickness control afforded by the atomic layer units is suggested to overcome the limitations of CVD in scaled-down semiconductor processes requiring ever thinner layers. Using ALD, it is possible to obtain a thin layer having a uniform thickness that can be finely adjusted to a precision of an atomic layer unit, and suppress generation of particles, a source of contamination.
However, the ALD process makes also use of a second reaction gas that is injected to induce reaction at high temperature, or that is ionized to convert a flux of plasma. At this time, charging due to ions or electrons may occur as a result of using the plasma. In addition, when the second reaction gas is injected as is, a second reaction gas process performed at high temperature is added to the ALD process.
Further, while a method of using remote plasma has been developed to solve the problem of charging, in such a method, flux and energy may be reduced.